In printing systems and processes, for example, digitally controlled printing systems and processes (such as an inkjet printing system and process), a print media is directed through a series of components. The print media can be a cut sheet or a continuous web. A web or cut sheet transport system physically moves the print media through the printing system. As the print media moves through the printing system, liquid, for example, ink, is applied to the print media by one or more printheads through a process commonly referred to a jetting of the liquid. The jetting of liquid onto the print media introduces significant moisture content to the print media, particularly when the system is used to print multiple colors on a print media. Due to changes in its moisture content, the print media expands and contracts in a non-isotropic manner often with significant hysteresis, a phenomena known as hygroexpansivity. The continual change of dimensional characteristics of the print media often adversely affects image quality. While dryers are frequently used to remove the added moisture from the print media, which reverses the moisture-driven expansion of the print media, drying can also cause changes in the dimensional characteristics of the print media that often adversely affects image quality. This is due in part to the drying process removing moisture from the portions of the print media that were not printed on, and also due to the hysteresis inherent in the hygroexpansivity process.
During an inkjet printing process, as the print media absorbs the water-based inks applied to it, the print media desires to expand. When the direction of expansion is in a direction that is perpendicular to the direction of media travel, it is often referred to as expansion in the cross-track direction. Typically, the wrap of the print media around a roller of an inkjet printing system produces sufficient friction between the print media and the roller that the print media is not free to slide in the crosstrack direction even though the print media are beginning to expand in that direction. This can result in localized buckling of the print media 10 away from the roller 52 to create lengthwise ripples, also called flutes 54, or wrinkles in the print media, as shown in FIG. 8. When the wrinkling of the print media during the printing process is severe, it can lead to permanent creases forming in the print media, which ultimately affects image quality.
Multiple printheads are typically located and aligned by a support structure to form a linehead; the linehead containing multiple printheads being located over the print media. In many such systems, the support structure of the linehead typically locates multiple printheads in two or more rows; the rows being parallel to each other and aligned with the crosstrack direction. To prevent the print media from fluttering, that is, vibrating up and down, in the print zone, the print media is supported by a roller that is aligned with the print line of each row of printheads. When printing at high speeds, it is not uncommon for the bottom face of the support structure to become wet, either due to condensation from the moist air produced by the printing process or due to mist drops created by the print drops striking the print media.
It has been found that, under some printing conditions, the flutes in the print media can be sufficiently tall that top of the flutes can contact the bottom face of the support plate. When this occurs, the moist ink on the flutes can be smeared by the contact. Additionally, the moisture on the bottom of the support structure can be transferred to the print media. The result is a degradation of the print quality.
As such, there is an ongoing need to provide printing systems and processes, for example, digital printing systems and processes, with the ability to reduce the print defects associated with excessive print media expansion produced by the absorption of water into the print media during the printing process.